Neuroscientists Say Gene Loosely Linked to ADHD

An fMRI showing the area of the brain associated with mind wandering or daydreaming.

November 17, 2010–A team of neuroscientists at Georgetown University Medical Center (GUMC) says brain scans show that a gene nominally linked to attention deficit hyperactivity disorder (ADHD) leads to increased interference in brain regions associated with mind-wandering during tasks.

The finding applies to issues of attention – sometimes called ADD – but not hyperactivity.

The researchers, who presented their findings at the Society for Neuroscience’s annual meeting Nov. 13-17 in San Diego, believe they are the first to show differences in brain network relationships between people who have this particular form of the gene and others who have a different kind.

Brain Networks

“Our goal is to narrow down the function of candidate genes associated with ADHD, and in this study, we find this gene is tied to competition between brain networks,” says Evan Gordon, the study’s lead author and a doctoral candidate in GUMC’s Interdisciplinary Program in Neuroscience. “This could lead to increased inattention, but it likely has nothing to do with hyperactivity.”

Chandan Vaidya, associate professor of psychology, served as Gordon’s mentor in the study funded by the National Institutes of Health.

Contributes, Not Causes

“This is just one gene,” Gordon adds, “and it does not cause ADHD but likely contributes to it. The disorder is believed to be due to a myriad of genetic factors."

The gene in question is DAT1 – its protein produces the dopamine transporter that helps regulate dopamine transmission between brain cells.

The DAT1 gene comes in two alleles, or forms – DAT1 10 and DAT1 9. People who inherit DAT1 10 are said to be at greater risk for developing ADHD than people with DAT1 9.

The researchers used functional MRI (fMRI) on a group of 38 participants. Half of the group had the greater ADHD risk type and half carried the other form. None of the participants had been diagnosed with ADHD.

Daydreaming and Problem-Solving

The researchers investigated the activity in two areas of the brain – the one associated with mind wandering or daydreaming that is active when the mind is at rest, and the area that is active during problem-solving and other cognitive work.

Participants were asked to remember letters they saw on a screen inside the fMRI machine, and to recall them, thus activating the latter area.

Memory Tasks

Scanning demonstrated that in those with the risk gene, the mind-wandering areas tended to communicate with regions involved in memory tasks more strongly than in did in those with the other gene type.

“Dopamine in the [risk gene carriers] was not doing a good enough job in preventing the mind-wandering regions from interfering with memory performance regions, resulting in less efficient cognition,” Gordon says.

The researchers also found no differences between genotype when the participants were at rest after their memory tasks.

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